New 6A crest factor setting in a WT300E power meter improves auto ranging capability and increases accuracy
For a Yokogawa power meter or analyser, selecting a crest factor of "6" means that the maximum peak voltage on a 150V rms range, for example, is 900 V. The accuracy of a WT300E power meter is specified from 1% to 130% of the range. Therefore with 1.5 V rms input on a 150V rms range, a crest factor of 600 is achievable.
This principle also applies to the current input ranges. When the rms value of the input current varies by a large amount and also the maximum current is not known, it is convenient to use the "Auto" ranging feature. Up to now, this has meant that the range changes up when the input current exceeds 130% of the range. The drawback is that while the range is changing, there is a short dead time when the instrument will not be able to make measurements.
When the new "6A" crest factor setting is selected in the Yokogawa WT300E, this is improved as the range will now change up only when the rms input current exceeds 260% of the range (or when the peak current is 600% of the range).
By reducing the possibility of a range change even when the security provided by the "Auto" ranging is used, measurement dead time is decreased and hence measurement accuracy, particularly for energy integration measurements, is improved.
